Magnesium comprises ¼ of iron and ⅔ of aluminum by specific gravity, and it noted as a metal having the smallest specific gravity as structural metals. In particular, magnesium base alloy has a higher rigidity than other metals, and is easier to lower in weight, and is developed in various applications as structural materials in various industrial fields (see, for example, patent document 1).
At the same time, owing to its excellent biocompatible properties, magnesium base alloy is being intensively developed in various industrial applications as medical materials, for instance, stent (see, for example, patent document 2)
However, magnesium base alloy is small in slip coefficient number at ordinary temperature, and is low in cold processability, and is hence actually limited in applications in a wide range, and in particular in the case of manufacture of a small-diameter magnesium base alloy tube used in manufacture of a stent, because of low processability, in order to obtain a large sectional area reduction rate, it is necessary to manufacture by way of a special manufacturing process, for example, by passing through multiple dice having tubular materials arranged in a row, and in addition to an extra cost required for manufacture, it is more likely to have affects of processing and hardening[[g, and it was hence difficult to obtain a small-diameter magnesium base alloy tube long in length, high in dimensional precision, and excellent in mechanical properties used for manufacture of a stent.